Method of forming combined metal and plastic article



Oct. 2, 1956 T. c. BEECH ETl'AL 2,765,248

METHOD OF FORMING COMBINED METAL AND PLASTIC ARTICLE Filed June 13, 1955ZNVENTORI moms c. ssscu y RICHARD T. BEECH mugma'r'foausvs United StatesFatent O METHOD OF FORMING COMBINED METAL AND PLASTIC ARTICLE Thomas C.Beech and Richard T. Beech, Roseviile, Mich. Application June 13, 195-5,Serial No. 515,092

3 Claims. (Cl. 154-110) been required in the manufacture of prototypesfor engineering developments and for display purposes, such as in theformation of automotive body moldings and other parts, have beenextremely expensive to fabricate and have required extremely longperiods of time to make the initial production. moldings, for example, anumber of the body parts such as bumpers, headlight rings, doormoldings, etc., have been required for engineering and display purposesand these parts had to be made by means of standard casting or stampingmethods. These methods are unusually expensive where only one or two orthree or four or other small numbers of parts are required.

An object of our invention is, therefore, to cheaply produce parts whichare suitable for the above purposes and provide a method for makingthese parts which require only a nominal amount of time and lowproduction cost.

Another object of our invention is to make small intricately shapedparts in dies which are inexpensive to make and which may be disposed ofafter use without loss of time or money and to provide a method fortreating these dies so that the metallic parts may be easily madetherein and more important may be easily removed there'- from.

In order to achieve our objectives, we prepare a die or mold out of someeasily worked material such as wood, plaster of Paris, gypsum basedplaster, and such similar type material. Thereafter, the mold or die istreated to first seal the pores of the mold and then with a partingagent which prevents the mold from sticking to the metal which will becast therein. Thereafter, an adhesive coating is provided in the mold sothat metal will stick to the mold until such time that it is decided toremove the metal from the mold.

Following the treatment of the mold or die, we then spray molten metalinto the mold to deposit a relatively thin shell of metal. The metalsheet, which is quite weak and which will not bear any load, isreinforced by a heavy layer of inexpensive plastic or in the alternativesuccessive sheets of glass fiber cloth and a resin binder.

After the formation of the article within the mold, the article may beremoved and then chrome plated by either covering the exposed metal withfirst a thin coating of copper, then a thin coating of nickel andfinally a thin coating of chrome or in the alternative by other suitablemeans.

It is thus apparent that the article when completed will give theappearance desired for a prototype or display model and will serve itsfunction adequately for engi- In the field of automotive body 2 neeringdesign purposes, but nevertheless the cost of the article will be quitelow. This reduction in cost is accomplished by means of the inexpensivedies required and by means of the use of only a thin metallic shellwhich is reinforced by relatively inexpensive plastic materials.

These and other objects of my invention will become apparent uponreading the following description of which the attached drawing forms apart.

Referring to the drawing in which:

Fig. l is a cross-sectional view of a mold or die in which our articleis to be formed.

Fig. 2 illustrates the formation of the metallic shell within the die ormold by means of a conventional spraying technique.

Fig. 3 is a cross-sectional view of the mold containing the metallicshell after the application of the plastic backing layer.

Fig. 4 illustrates a perspective view of an automobile type moldingwhich may be formed by our process.

Fig. 5 is a cross-sectional view of a portion of the molding illustratedin Fig. 4 and is enlarged to illustrate the glass fiber cloth sheets andthe resin binder which may be used to reinforce and back up the thinmetallic shell.

As previously mentioned, the object of this invention is to formintricately shaped metal parts inexpensively and quickly. To this end,our invention contemplates forming a die or mold within which thearticle may be molded. Referring to Fig. 1, a suitable mold 10 isprovided with female cavities 11 which are complementary to the exteriorsurface of the molded article. This mold or die may be made of anysuitable material such as plaster of Paris, a gypsum based plaster,wood, or other easily workable material. The mold itself may be hollowedout or cut out to form the cavities 11 by any known and suitable shoptechnique.

Treatment of the mold Once the cavities are formed in the die, and priorto depositing the metallic shell therein, it is desirable to treat thecavity surfaces in order to first seal off the pores of the mold or diematerial to prevent moisture seepage which may harm the metal shell, andto thereafter apply a parting agent to insure that the metal depositedwill not stick to the mold when it is desired to remove the metal fromthe mold. Moreover, in the spraying of thin walled metallic shells, whenthe metal is sprayed into contact with the mold walls, the metal has atendency to shrink away from or move away from the cavity walls. Thisresults in a finished product which is not truly correct in dimension.To solve this problem and insure contact between the metal and moldcavity during the time of spraying and cooling of the metal, we apply asuitable adhesive over the parting agent which adhesive adheres to andholds the metal, as it is sprayed, in its proper relationship to thecavity walls.

Although a number of materials are suitable to accomplish the abovefunctions, we have found at least one material which is suitable foreach function and therefore will give an example of each one of thesematerials below.

Where the mold is made of a gypsum based plaster or some such similarplaster material, we have found that a coating of cellulose base lacquerfirst applied to the mold and then allowed to dry thoroughly will tendto seal the pores of the mold and seal in the moisture. Thereafter, wetreat the mold with a carnauba base emulsion in a mineral spiritsolvent. This material is commonly known as wax and is of a specifictype of wax. The wax film is applied and polished once or twice or moreas the case may be to provide a smooth surface for the reception of themetal deposits.

An example of one type of wax which is suitable for this purpose is asfollows:

Carnauba base 11.25% Soap 0.75% (emulsifying agent) Mineral spiritssolvent remainder it should be understood however, that we do not limitourselves to the particular wax described above but only give thisdescription by way of an example to suggest one type of wax which issuitable for this function.

Also, by way of example, one type of compound which has been foundsuitable for sealing in the moisture in the mold is as follows:

A polymerized vinyl alcohol in an ethyl alcohol, water, nonyl alcoholsolution which is then sprayed .on the mold. This material may becompounded in the following parts:

Polyvinyl alcohol 100 parts Ethyl alcohol 100-150 parts/100 Water 2030parts/ 100 PVA Nonyl alcohol 3-5 parts/ 100 PV A The above compoundfunctions as a sealing agent so that the metal sprayed can be easilyremoved from the mold when it is so desired.

Thereafter, after the above polymerized 'vinyl alcohol etc., is driedthoroughly, a neoprene phenolic type adhesive with a suitable solvent,such as toluene, to act as a vehicle, is sprayed over the entire moldsurface and this adhesive functions to keep the sprayed metal in contactwith the mold wall.

One example of the chemical compositions of such an adhesive is asfollows:

Neoprene phenolic type adhesive in which there is present 65 to 85 partsby weight of pheno aldehyde resin to 100 parts of polychloropene with,l85225 parts of toluene as a vehicle. This type of adhesive is set forthin United States Patent No. 2,610,910.

Once again it is to be understood that our desire is to provide first asealing compound to seal the pores of the mold, second a wax base whichmay be polished to completethe sealing and also to provide a smooth wallsurface; then a parting agent, and finally an adhesive which will holdthe sprayed metal in place until removal is desired.

PVA

The metal spraying The metal shell of the article to be made isdeposited within the treated mold by means of a suitable spray process,such as the i ell-known Schoop process, in which a spray gun depositsmolten metal by means of compressed air or other air pressure. Thusreferring to Fig. 2, it can be seen that the shell 12 is being depositedby means of a standard and conventional spray gun E3. The actualspraying of the metal is well-known in this art and therefore nodetailed description of either the spray gun or the exact method ofspraying is necessary.

However, in our process, we make it a point to provide a dense surfaceof the metal which is exposed. The reason for this dense surface is topermit chrome plating to later be accomplished. In order to properlychrome plate an article, it is important that the outer surface of thearticle be as dense as possible. Therefore, we spray the first one-thirdof the'metal shell at approximately 80 p. s. i., the next one-third at70 p. s. i. and the last onethird at approximately 5 0 p. s. i.

The lower the pressure, the faster the spray process may proceed. Thereason for this is that the high pressure air tends to blow the moltenmetal out of the mold and out of proper place. Therefore, the firstone-third of the mold is sprayed at a high p. s. i. despite the factthat it takes much longer to do so in order to achieve a very denseouter surface. Thereafter the next onethird is sprayed at a lowerpressure whereby although the density of the metal is reduced, theprocess is speeded up.

Finally, the last one-third or the inside one-third of the metal shellis sprayed at a relatively 'low pressure in order to quickly finish thejob and particularly so since it is not important whether the insidesurface be of high density or low density.

Any metal which may be sprayed into this mold is suitable for ourpurposes and such metal may be zinc, copper, iron, etc. The temperatureof spraying is nor: mally prebuilt into the spraying gun and thereforeforms no part of this invention. However, it is only important that thetemperature be "sufficient to melt the metal and to permit its ejectionfrom the gun into the mold.

The metal shell when completed is quite thin and in many of the articlesdesired, for example, in the auto motive parts industry, need only be inthe range of approximately A Obviously, the thickness of the metal canbe considerably less than ii or in the alternative can be somewhat more.However ,-it is an'object of our invention to reduce the thickness ofthe metal to speed up the process and make the job less expensive.

The plastic hacking The metal shell because of its thinness is extremelybrittle and weakand may be easily broken or damaged in removal from themold. Moreover, it would serve no useful function .once removed from themold because it would lack the strength necessary for use in engineeringand design tests. Therefore, we provide a relativethick layer of plasticmaterial 20 inside the shell 12 in order to reinforce the shell and giveit adequate strength for ordinary use.

With reference to Fig. 5, we have found that we can obtain an extremelystrong plastic backing for the metal shell 12 by means of the use ofglass fiber cloth sheets. Thus, one Way of reinforcing the shell wouldbe to use successive sheets of open weave glass cloth. Preferably, forour purposes, we use a chrome-complex open weave glass fiber cloth.Along with this cloth, we use a low pressure laminate using an epoxyresin compound such as bisphenol in combination with epichlorohydrincured with 25-30 parts of an amine type hardener to each parts resin.The resin backing is cured at room temperature.

Fig. 5 shows a portion of sample molded article, in this case, anautomobile molding strip 21, wherein the plastic backing 20 comprisesthe fibrous glass sheets 28 and the resin 29. In addition, the chromeand other metal coatings which are placed on the outside of the shell 12are generally designated as 25, for simplification purposes.

It is desirable to form the plastic backing in the shell while the shellis still hot so that the resin tends to fill the open pores of the lowdensity inner surface of the shell and thereby coact therewith to form atight bond between the plastic and the shell. Moreover, once the plastichardens, it prevents the shell from losing its desired form. a 7

Chrome plating the article After the metal shell cools and the plasticbacking is cured at air temperature, the article is removed from themold. This removal is accomplished quite easily due to the action of theparting agent.

Thereafter, it is normally necessary to chrome plate the article whereit is to be used for display purposes or as a part of a prototype whichis chrome decorated. The

chrome plating process may be done either by dip coat ing or byelect'ro-plating.

The surface of the shell is prepared for the chrome plating by firstcopper plating the dense outer surface to' critical and actually mayvary considerably without any undesirable effects. It is only to benoted that the thicker the coating, the more expensive the article.

Thereafter, the copper coating is nickel plated, also by anyconventional process, such as by dip coating the copper with a fewthousandths of an inch of nickel or a nickel bearing alloy. The functionof the nickel is to give the bright shiny color to the article which isdesirable as mentioned above.

Thereafter, the part is chrome plated again either by dipping or in somecases by electro-plating to get approximately ,4 of a thousandth of aninch thickness of chrome, more or less, to thereby complete the articlefor use.

The thicknesses of the above metallic coatings are not critical by anymeans and therefore may be varied considerably. Moreover, as mentionedbefore, the thickness of the metal shell is likewise not critical but isnormally kept quite thin for economy reasons. 5 the thickness of theplastic layer within the shell is dictated only by the requiredstrength. In an article such as a bumper, which should be fairly sturdyin order to hold up in display purposes and under engineeringexplorations on an automobile, should be relatively thick.

Con clusion It can be seen that by means of our process, we can produceinexpensive molded articles comprising plastic and metal which articlesare strong and relatively durable and which are well suited for use inengineering tests, prototype constructions and display purposes. Ourprocess obviates the necessity of expensive dies and expensive tools toform the article. Moreover, we utilize conventional spraying equipmentto spray metal to form the article and therefore require no specialtooling for that purpose.

In addition, the article which is formed of only a thin shell of metal,because of its plastic backing and because of, Where desired, thesuccessive sheets of glass fiber, is extremely strong and will take thenormal wear and tear upon such models. Further, our model can be easilychromed in order to give a finished appearance.

By means of the use of the treating steps which include sealing, we areable to use such sheet mold materials as plaster of Paris or gypsumplaster. In addition, by means of first Waxing the interior of the moldso as to form an extremely smooth surface, and then spraying the metalat a high pressure to form a high density outer surface, we obtain notonly a surface which can be easily chrome plated but which also issmooth and finished looking. Thereafter, We are able to reduce costs andat the same time provide a porous inner surface to which the plasticbacking may adhere, merely by the use of a lower spraying pressure.

Further, our process eliminates the possibility of the metal shellspringing away from or drawing away from or shrinking away from the moldcavity walls by means of the use of a parting agent which permits theseparation of the metal from the mold and by the use of an adhesivewhich effectively glues or adheres the metal to the parting Zhe variousmaterials ntioned in conjunction with each one of the functions requiredare not critical and it necessary only that these materials suitablyperform functions. The examples given in the above description aremerely each examples of a material which performs the function and areby no means a limitation on our invention.

This invention may be further developed within the scope the followingclaims. Accordingly, it is desire that the foregoing description be readas being merely illustrative of one method of carrying out ourinventions and not in a strictly limiting sense.

Now having described one operative embodiment of our invention and oneoperative method for carrying forth our process, we now claim:

l. A method of die forming, in an inexpensive easily worked mold,articles having a relatively thin metallic shell with a dense outersurface and formed into various curves and backed by a thick layer ofplastic bonded to the shell to rigidify and strengthen the shell,comprising steps of: forming a die with an open die cavity f om aneasily worked porous material; sealing the pores of the die materialwithin the cavity with a sealing material; forming a metallic outershell by spraying molten metal into the die cavity against the cavitywalls under high pressure to form a thin, high density surface incontact with the die walls, and continuing the molten metal spray underlow pressure to quickly form a less dense and porous metallic backingfor the outer metallic surface; immediately thereafter, while the shellis still hot, depositing under ordinary atmospheric conditions of pressure and temperature a thick backing layer of a noninetallicthermoplastic material Within the shell to thereby bond the plasticmaterial and the shell together; and finally, removing the article fromthe die.

2. A method as defined in claim 1 and including the step of coating thecavity walls with an adhesive material before forming the shell to causethe shell material to adhere to the cavity walls at all places duringthe formation of the article and before removal thereof from the die.

3. A method as defined in claim 1, and said layer of thermoplasticmaterial be" g formed by successively placing sheets of glass fibercloth and a thermoplastic resin binder into the shell and against theshell inner walls to build up a thick backing layer.

References Cited in the file of this patent UNITED STATES PATENTS1,688,645 Novotny Oct. 23, 1928 2,343,225 Pray et al. Feb. 29, 19442,349,920 Welcome May 30, 1944 2,439,137 Keller Apr. 6, 1948 2,476,994Milton et al. July 26, 1949 2,638,428 Gordon et al. May 12, 19532,747,180 Brucker May 22, 1956

1. A METHOD OF DIE FORMING, IN AN INEXPENSIVE EASILY WORKED MOLD,ARTICLES HAVING A RELATIVELY THIN METALLIC SHELL WITH A DENSE OUTERSURFACE AND FORMED INTO VARIOUS CURVES AND BACKED BY A THICK LAYER OFPLASTIC BONDED TO THE SHELL TO RIGIDIFY AND STRENGTHEN THE SHELL,COMPRISING THE STEPS OF: FORMING A DIE WITH AN OPEN DIE CAVITY FROM ANEASILY WORKED POROUS MATERIAL; SEALING THE PORES OF THE DIE MATERIALWITHIN THE CAVITY WITH A SEALING MATERIAL; FORMING A METALLIC OUTERSHELL BY SPRAYING MOLTEN METAL INTO THE DIE CAVITY AGAINST THE CAVITYWALLS UNDER HIGH PRESSURE TO FORM A THIN, HIGH DENSITY SURFACE INCONTACT WITH THE DIE WALLS, AND CONTINUING THE MOLTEN METAL SPRAY UNDERLOW PRESSURE TO QUICKLY FORM A LESS DENSE AND POROUS METALLIC BACKINGFOR THE OUTER METALLIC SURFACE; IMMEDIATELY THEREAFTER, WHILE THE SHELLIS STILL HOT, DEPOSITING UNDER ORDINARY ATMOSPHERIC CONDITIONS OFPRESSURE AND TEMPERATURE A THICK BACKING LAYER OF A NONMETALLICTHERMOPLASTIC MATERIAL WITHIN THE SHELL TO THEREBY BOND THE PLASTICMATERIAL AND THE SHELL TOGETHER; AND FINALLY, REMOVING THE ARTICLE FROMTHE DIE.